Multiple radio recorder



Feb. 22, 1944. J. T. POTTER MULTIPLE RADIO RECORDER Filed Feb. 23, 19393 Sheets-Sheet 1 INVENTOR J/ua ZZPoZ-Z'er WWW ATrOR NEY Feb. 22, 1944.J. T. POTTER 2,342,167

MULTIPLE RADIO RECORDER Filed Feb. 23, 1939 3 Sheets-Sheeb 3 759- I5! 1g I55 ig I24 122125' '34 INVENTCR John If Pofiier saw/WM ATTORNEYPatented Feb. 22, 1944 UNITED STATES PATENT OFFICE MULTIPLE RADIORECORDER John '1. Potter, Brooklyn, N. Y.

Application February 23, 1939, Serial No. 257,984

4 Claims.

The present invention relates to recorders and in particular to methodsof and means for recording the operation of a plurality of radioreceivers.

One object of the present invention is to record at a central point andon a single re ord sheet the tuning and operating conditions of aplurality of radio receivers located at remote points.

Another object is to provide such recording in accordance with spacedimpulses of audio or super-audible alternating current voltage whereinthe time relations of the impulses indicates the information to berecorded.

A further object is to provide greater sensitivity and selectivityagainst noise and hence to make greater recording distances possiblethan hitherto available.

Still another object is to provide an impulse generator to be connectedto the radio receiver which sends out an impulse of considerable powerover a short interval while requiring only a small input power at anygiven instant.

Another object is to generate at the radio receiver an impulse of shortduration and of a frequency which varies thru a narrow range in or derto make useful a high degree of frequency selectivity at the centralstation and yet permit some drift in average frequency of the generatedimpulses.

In the copending application entitled Multiple recorder, now PatentNumber 2,249,324, issued July 15, 1941, is shown and described arecorder adapted to record the tuning and operation of a plurality ofradio receivers on a single record sheet. At each radio receiver acommutator turns on a fixed frequency oscillatorfor a short intervalwhich is spaced within a second and longer interval in accordance withthe tuning'conditions of the receiver. The longer intervals are equalfor the various receivers and are phased so that they are consecutivebut do not overlap. The longer intervals for all the receivers may addup to a convenient recording time cycle as for instance one minute. Atthe recorder signals generated by the various radio receiver recorderoscillators are amplified by a fixed frequency amplifier and recorded ona record sheet which is conveniently in the form of a cylinder whichmakes one revolution per recording cycle. Thus the operation of aparticular receiver is recorded in a unique column axially of thecylinder and the reception of a particular station by the receiver isrecorded in a line within the column.

'I'hegeneral' system employed in the present invention is the same asgiven above but certain novel improvements have been made. In order toincrease the sensitivity of the recorder amplifier in order to permitgreater recording distances and also in order to increase theselectivity of the amplifier against noise and other interferences theamplifying is done in two distinct stages at different frequencies. Thereceived signals are first amplified with as much gain and selectivityas is economical and practical and then the signals are heterodyned to alow frequency and again amplified with a large amount of gain andselectivity. The second frequency is chosen as low as possibl consistentwith the presence of normal amounts of harmonies of the localalternating current power lines and other line noises.

At the radio receivers a substantial improve.- ment has been produced bystoring energy during periods between impulses and releasing it inaccordance with the information to be recorded. In addition, thefrequency of the impulse is varied slightly during generation in orderthat the high degree of selectivity of the recorder amplifier may beuseful in the presence of nominal amounts of drift in average frequencydue to temperature and other frequency changing effects.

In the drawings:

Fig. 1 shows a schematic diagram of a recorder embodying the presentinvention.

Fig. 2 shows a radio receiver impulse generator unit embodying mypresent invention.

Fig. 3 shows a detail of the recorder.

Fig. 4 shows an additional recorder detail.

Fig. 5 shows a circuit detail.

Fig. 6 shows a method of phasing the receiver units.

Fig. '7 shows an auxiliary impulse generator useful in phasingoperations.

Fig. 1 shows a complete central station amplifler and recorder. Whileother methods of transmission may be used the description will beparticularly in connection with transmission of recording signalimpulses over alternating current power lines common to the radioreceivers and central recording unit. Lines and 2 are connected to thelocal power lines. Fuses 3 and 4 are provided to protect the apparatusin case of short circuits within it. Wires 5 and 6 go to primary I of aconventional power supply transformer for supplying heater current tothe various amplifier tubes and direct current for the plates and gridsof the tubes and for the recording magnet 99. Branch wires 8 and 9connect transformer primary I2 to the power line thru blockingcondensers I9 and H. Secondary I3 is coupled to primary i2 and is tunedto the operating frequency of the radio receiver impulse generatingunits shown in Fig. 2, which may conveniently be of the order of 100kilocycles. The selected voltages appearing across secondary I3 areapplied to grid I9 of pentode amplifier tube I5. The output of tube I5appearing at its plate 22 is further selected by tuned load circuits I7I9 and the coupled tuned circuit l9-29 all tuned to the same generatedfrequency. The voltage across coil I9 is applied to the second amplifiertube 2I at its grid 23. Output voltages on plate 24 are again selectedby tuned circuits 2526 and 2'I--28 and applied to grid 33 of themultigrid converter tube 35. Cathode 29, control grid 39 and anode grid3| of tube 35 function With transformer 3'I38 tuned by condenser 49 toproduce heterodyning oscillations at a desired difierence frequency withsaid generated frequency as for instance 95 kilocycles. The 5 kilocyclediiference frequency appears at plate 34 and across plate load resistor49. Since the 95 and 100 kilocycle voltages-"are no longer desired theyare eliminated by means of the filter composed of choke 45 and'condenser41. The 5-kilocycle voltage to be further amplified and utilized tooperate the recorder is'applied to grid 49 of amplifier tube 59 by meansof a tap on volume control 93 thru blocking condenser 49. The amplified5 kilocycle signal on plate 5i is made large by loading plate 5I withinductance 53 tuned to 5 kilocycles by means of condenser'52. The signalvoltage across inductance 53 is applied to grid 99 of am-' plifi'er tube57 thru blocking condenser 59 and across grid resistor 55-. Amplifiertube 51 is a triode particularly suited to-operate a diode rectifier.The amplified signal on plate 59 loaded by resistor 99 is applied to adiode rectifier con-v sisting of plates 59 and cathode 99 ofdiode-triplate 98 is passed thru magnet 659 of the recorder unit andthus operates pen 92. The recorder consists in cylindrical drum coveredby a record sheet I9 mounted on a shaft I5 and driven by synchronousmotor 11. Motor ll is operated from the same alternating current sourceas the radio receiver signal generating units in order to providesynchronous operation. Magnet 69 is moved along the recorder'drumby thelead screw 8| driven from sprocket 89-by chain 78 and a sec ond sprocketI9 on motor'shaft I5. Motor ll includes suitable reducing gears toproduce a speed of shaft I5 of the order of one revolution per minute.Sprockets 'I9and 99 are proportioned so that with a properly chosenpitch in lead screw BI magnet 99 is caused to traverse the drum in asuitable time as for instance 24 hours. In order to produce an equalmarking intensity regardless of the strength of received signals pen 82is operated by gravity. Plate current in tube 61 is adjusted by properchoice of bias battery 94 voltage so that magnet 69 is energized and pen92 is kept ofi of the record sheet inthe absence of received signals.Received signals are rectified and applied to grid 95 as negativeimpulses causing magnet 69 to release allowing pen 82 to contact recordsheet I6. Control 48 is used to set therecording level abovethe noiselevel.

In Fig. 2 is shown a circuit diagram of an impulse generating unitsuitable for attachment to a radio receiver for generating impulsesindicating the operation and tuning conditions of the receiver to berecorded at the above described central or recording station. Theimpulse generator comprises a thermionic vacuum tube oscillator and amotor driven contactor sweeping over a commutator connected to amulti-point switch associated with the radio receiver tuning mechanism.The oscillator circuit utilizes a vacuum tube 99 having a cathode 99,control grid and plate 97. This tube is connected to an oscillatorycircuit made up of grid coil 99 tuned by condenser 92, plate coil 89coupled to grid coil 99 and tuned by condenser SH, and grid resistor 93Joy-passed by grid condenser 94. This constitutes a feedback oscillatorwith grid and plate tuning. Oscillator voltage impulses are fed to thelocal power line by means of coil 88 coupled to plate coil 89, blockingcondensers 8'I-89 and line plug 83.

Cathode 93 is energized from the filament transformer secondary 99 theprimary I99 of which is also supplied from the power line thru leadsI9I, I92 and I99 and relay contact I98, so that tube 99 is operable onlywhen relay I9II98 is closed. Plate voltage for tube 96 is supplied fromcondenser II2 which is charged thru resistor II9 from the high voltagedirect current source I93 of the radio receiver I44 being monitored thrulead I94. Oscillator tube 99 is rendered inoperative further by platecurrent cut-off bias applied to heater source '99 from resistor I I Iand through resistor H3. Resistors III and H3 are proportioned to keepplate current to tube 96 substantially cut-oil or at least small enoughso that the tube 99 does not oscillate. Resistor H3 is shorted atintervals in a manner to be described thus removing the cut-off biasfrom tube 96 and causing it to oscillate strongly dissipating the chargein condenser I I2. denser II2 recharges thru resistor H9 to essentiallythe voltage of source I93. Since the periods of oscillation are veryshort compared to the periods between oscillation the average chargingcurrent. drawn from source I93 may be made small compared to the currentdrawn for the short oscillation intervals from condenser I I2. As anexample the intervals between impulses may be 109 times the periods ofthe impulses and tube 99 may draw 1G0 milliamperes during theoscillation periods while drawing only 1 milliampere from source I93.This provides efficient operation and permits operation of a powerfuloscillator from a small capacity power supply without disturbing thenormal operation of the power.

supp y.

Radio receiver I44 is to be monitored. It is connected to antenna A andground G or other suitable energy collecting means. While other types oftuning mechanism may be monitored, for purposes of explanation avariable tuning j condenser I29 is shown in receiver I44. 0n theelectrical connection between contactor MI and.

common output lead I28. The switch also-in cludes end supports I38 andI39 and anchor wire. or string I99 forrestraining longitudinal motion ofthe switch. Wire or string I49 may be fe s tene d Between intervalsc0n-.

to a suitable and convenient point of the chassis or cabinet of I44 sothat the switch body is held in a line substantially tangent with pulleyI3I. Contacts I32, I33, I34, I35 and I36 are adjusted on a particularreceiver so that as condenser I29 is tuned contactor I4I makes contactwith them at condenser settings corresponding to radio stations whichare to be recorded.

Timed impulses are generated by means of a motor driven commutatoroperated in connection with the switch and oscillator described above.The commutator comprises commutator points I22, I23, I24, I25 and I26connected to switch points I32, I33, I34, I35 and I36 respectively;motor driven commutator arm I2I; and synchronous motor II6 connected tothe power line by meansof leads H4 and H and line plug 83. Arm I2I isdriven at a convenient speed as for instance one revolution per minutethru reduction gear box 1. Gear box II! is mounted on a plate H8 havinga semi-circular slot H9 and the said plate is clamped to motor II6 bymeans of screw I20. The phase relation of arm I2I with respect to thealternating current power line voltage may be adjusted by releasingscrew I20, turning plate II8 to a desired position and replacing screwI20. Commutator segments I22 to I26 inclusive are equally spaced andoccupy a predetermined angle as for instance six d grees. As arm I2Irotates it completes a circuit thru the receiver condenser operatedswitch and leads i2! and I28 corresponding to the position of contactorMI and hence condenser I29 and the time and phase relation of arm I2Ishorting cut-on bias producing resistor I I3 and causing tube 96 tooscillate feeding an impulse of oscillator voltage to the power line.The additional commutator point I45 is connected to the common switchlead I28 so that at each rotation of the commutator arm I2I a signal isgenerated indicating that the radio receiver is turned on Whether or notone of the preselected stations is tuned in.

The operation of a system including a number of receivers will now bedescribed. A particular receiver I44 is turned on by a listener. Whenthe receiver has warmed up voltage appears in source I63 energizingrelay coil I01 closing contact I08 and thus energizing filament orheater 98 of tube 96. At the same time condenser II2 starts to chargethru resistor IIO until it reaches the voltage of source I03. Motor II 6is operated continuously and every minute sweeps contacts I22 to I26inclusive with arm I2I. If receiver I44 is tuned to a station thereception of which is to be recorded one of these commutator points I22to I26 is energized thru contact MI and one of the contacts I32 to I36inclusive. When arm I2I contacts an energized segment, resistor H3 isshorted and an impulse of oscillator voltage is applied to the powerline. This impulse-is received at the central station and recorded onthe record sheet by the central station amplifier and recorder describedabove. While tube 96 is oscillating, it is drawing a heavy current fromcondenser II2 causing the voltage across it to fall. This fallingvoltage causes the oscillator frequency to vary slightly. For instance,a central station may be tuned accurately to 100 kilocycles while theoscillator may oscillate from 99 to 101 kilocycles. It will be seen thatthe mean frequency may vary plus or minus 1 kilocycle and it will stillpass thru 100 kilocycles while it is being impulsed. This frequencyvariation permits a high degree of selectivity to be used in impulse ispicked up and the central unit and a variation of the oscillator meanfrequency and still proper recording of the signal will be accomplished.

With the commutator segments occupying six degrees, for instance, sixtyreceiver units may be operated into a single recorder without overlap byphasing the receiver impulse generating units to be complementary intime spacing. This spacing and mode of operation is more particularlydescribed in the co-pending application cited above.

In a radio receiver recording system, such as the one herein described,it is important that further recording be prevented in case of momentarypower failure since in general such failure will destroy the properphase relations between the receiver units and the central stationrecorder. Fig. 5 shows a relay I45i46I4'I- I 48I50 which is interposedbetween the power source wires 8485 and the leads IOII02 and II4-II5going to the oscillator tube filament transformer 93I60 and thecommutator motor II6 respectively. This relay is designed to closecontact I48 energizing the oscillator and motor as long as the power isuninterrupted but opens and stays open until reset in case of temporarypower failure. From power supplied through the current limiting resistorI43 relay coil I46 energizes core I45, attracting armature I41 againstspring I50, thus closing contact I48.

Fig. 6 shows a method of phasing the various receiver units. An impulseis transmitted once for each revolution of the commutator arms I2I, I2I,IZI etc. by apparatus as in Fig. 7. This the operator listens to it in apair of earphones. Each receiver unit is provided with an auxiliary armI56, I 56, I56" etc., each phased by a different angle with the maincommutator arms IZI, I2I, I2I" etc. The difierence angles a, b, 0, etc.,differ by the angle a subtended by the commutator contacts I22, I23,I24, etc. The auxiliary commutator arm is adapted to short a pair ofcontacts I54I55 in each unit completing a circuit thru leads I58 I59 andline plug I6I to a neon lamp I60. Each receiver unit is phased until theneon lamp I60 flashes in synchronism with the impulses received in theearphones. When all the units are so phased, they will operate at therelative phase angles determined by the auxiliary arms I56, I56, I56",etc., which have been predetermined to be the desired phasing angles.

Fig. 7 shows an impulse generator I66 having a single synchronouslydriven commutator arm I64 driven at the same rate as arms I2I, I2I', I2Ietc. Arm I64 shorts contacts I62I63 and by turning on an oscillator orother suitable means, sends the phasing pulse over the power line bymeans of wires I 6'II 68 and line plug I66. This phasing pulse isgenerated while the various receiver units are being set up and phasedor in case of power failure for rephasing purposes and is turned offwhile recordings are being made.

While one embodiment of this invention has been shown and described, itis intended to limit it only in accordance with the spirit and scope ofthe invention as set forth in the appended claims.

I claim:

1. In a radio receiver tuning condition and operation determiningsystem, the combination of, a selector switch adapted for selectiveoperation in response to the tuning condition of the radio receiver, anormally inoperative oscillator, a motor driven commutator for renderingsaid 'oscillator operable 'in'accordance with the position of saidselector switch, and a condenser and resistor connected to said radioreceiver and receiving current therefrom for storing energy at asubstantially constant rate to provide power for energizing saidoscillator during its periods of operation.

2. In a radio receiver tuning condition and operation determiningsystem, the combination of, a selector switch adapted for operation inresponse to the operation and tuning of the radio receiver, a normallyinoperative oscillator, a motor driven commutator for rendering saidoscillator operable in accordance with the position of said selectorswitch, a condenser for continuously storing energy for energizing saidoscillator during its periods of operation, a source of direct currentwithin said radio receiver, and a resistor connected between said sourceand said condenser for limiting the current supplied to said condenser.

f 3. In a radio receiver tuning condition and operation .determiningsystem, the combination of, amulti-point switch adapted for operation inresponse to predetermined tuning conditions of said radio receiver, anormally inoperative oscillator, means for rendering said oscillatoroperable at predetermined time intervals in accordance with the positionof said multi-point switch, means for deriving electrical energy fromthe radio receiver, means for storing said energy for energizing saidoscillator during the time. of inoperativeness of said oscillator, andmeans for releasing said stored energy during intervals of operativenessof said oscillator.

4. The system as claimed in claim 1, and means for rapidly varying thefrequency of said oscillator through a selected frequency.

JOHN T. POTTER.

